Synthetic type 1B yellow diamonds containing nitrogen in single substitutional form, with extremely low birefringence, were used as anvils in a diamond anvil cell. The diamonds were well characterized by infrared and visible absorption spectra. Sensitive spectroscopic methods along with mechanical chopping techniques were used to record ruby fluorescence to 250-300 GPa, a pressure equal to or exceeding that attained with natural diamonds. Nitrogen platelets are not essential to attaining multimegabar pressures.
